1. Field of the Invention
The present invention concerns a system for controlling the flaps of a turbine engine nozzle.
2. Description of the Prior Art
Turbine engine nozzles whose section can be adjusted according to the engine speed by means of displacement of flaps in the form of movable wall elements, have been known for a long time. Applicant's French Pat. Nos. 1,215,236 and 1,215,237, for example, disclose nozzles equipped with pivoting flaps making it possible to regulate the nozzle section as well as to modify the nozzle contour from a converging shape suitable for subsonic flows to a convergent-divergent shape suitable for supersonic flows, and vice-versa.
Thrust reversers for turbine engine nozzles, which also include movable flaps, are also known.
Many types of systems are known which make it possible to control the flaps of a turbine engine nozzle. Some of these known systems include hydraulic jacks for controlling the movable flaps; they are fed with fuel or with a standard hydraulic liquid by a pump selected so as to meet the system's operating conditions. According to their operation, the hot gases leaving the nozzle apply pressure on each flap, which tends to make it pivot radially outward, further separating the flap from the axis of the nozzle. This pressure exerted on each flap is relatively low when it is in its position corresponding to the maximum opening of the nozzle, and is much stronger when each flap is in its position corresponding to the minimum opening of the nozzle (or in its complete closure position in the case of thrust-reverser flaps). The pump's delivery pressure must therefore be much higher in the second case than in the first. Furthermore, the pump must be able to supply a considerable flow during the short periods of transitory speed of the turbine, during which the flaps of the nozzle must be brought from a position corresponding to the maximum opening of the nozzle to a position corresponding to the minimum opening of the nozzle. In contrast, during steady operation of the turbine engine, the pump need supply only a weak flow corresponding primarily to the fluid loss from the hydraulic jacks.
In order to attempt to satisfy these various operating conditions, pumps of various types have already been utilized, each driven mechanically by the shaft of the turbine engine either directly or through an appropriate transmission. Thus, self-regulating constant-capacity, positive displacement pumps have already been utilized in association with modulator valves intended to recycle the excess fraction of the flow from the pump.
All these systems have in common the drawback that the speed of the pump and the flow remain high, even at steady speed, causing wear and overheating. In addition, the modulator vlaves give the system a response time that is too long at transitory speeds.
The use of a constant-capacity, positive displacement pump has also been tried in association with a jet valve; the stability of such a system is not yet certain, however. Associating two displacement pumps has also been thought of, with one constantly sending a weak flow of hydraulic liquid or fuel into the jack to compensate for fluid loss in steady operation, while the flow delivered by the other displacement pump is recycled, except during transitory speeds when it is likewise sent into the jack. Such a system is obviously heavy and costly. Variable-output pumps which are also able to reverse the direction of the flow have also been utilized. Such systems are however relatively complex and various accessories, such as pressure regulators, must be associated with them. Finally, the idea arose of associating a relatively low-output (but sufficient for steady operation) displacement pump with a hydraulic accumulator which was only put into use during transitory speeds. However, this solution assumed that the intervals between successive transitory speeds, i.e., between successive maneuvers of the movable flap, were sufficient to allow recharging of the accumulator.